The differential pressure transmitter shows fluctuations in liquid level measurement
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The differential pressure transmitter is used to measure the liquid level in the bottom of the distillation tower; when the system pressure fluctuates slightly, the liquid level experiences significant changes, and the gas phase pipe is 3 meters above the bottom of the tower! What is causing this?
The differential pressure transmitter is of the double-flange type, right? Could you share the diagram of the tower’s structure as well as the inlet and outlet pipelines so I can study them? Otherwise, I don’t know where to start
There are quite a few reasons; the information you’ve provided is too limited. I think there could be issues such as an abnormality in the negative pressure chamber of the gauge (maybe something is blocking it), or changes in the liquid level within the tower itself. In any case, after calibrating the gauge, the issue related to the gauge itself can be ruled out. It’s hard to say anything definite without further analysis……
After opening it, there is no liquid in the pressure guide tube – only gas! There’s no dirt either; our equipment are devices used in laboratories! The pressure lead tube of the differential pressure transmitter is 1/2 inch in diameter. During initial testing it performed stably; however, when the pressure became too high, some of it was released and as a result the reading fluctuated by 70%, dropping to 40%. After removing the pressure lead tube and releasing some air, normal operation was restored! So I don’t understand why; the raw material is isobutylene, which is distilled.
The pressure fluctuations inside the tower have different intensities and delays in their impact on positive and negative pressure measurements, which results in large fluctuations in the liquid level measurement signals.
In simple terms, when there is a change in pressure, the pressure on the positive and negative sides becomes uneven; in other words, it isn’t applied to both sides at the same time. It is recommended that you make some modifications and give it a try – add a condensation tank on the negative side and fill it with condensate to see if that helps
Thoroughly remove all air from the pressure guiding tube and the measuring diaphragm of the transmitter by using the small drain screw located at the back of the transmitter
I’ve seen people say there is a delay; that’s possible as well. First, consider the issue from the perspective of the instruments, and only after ruling out any problems with the instruments should we consider process-related issues. It is recommended to check whether all the valves associated with these instruments are functioning properly, and it’s also advisable to take these instruments to a calibration station to check their linearity. A pressure tap is being used; the threaded part of the pressure tap must not leak air. Is it connected via a three-valve assembly? Is a distillation tower a vacuum distiller? Does the pressure inside the tower fluctuate? Is the double-flange level gauge of the pressure-transmitting tube type? So the pressure tapping pipe at the lower end measures the liquid-phase pressure, while the one at the upper end measures the gas-phase pressure? Is the gauge below the lower opening? Also, on the liquid phase side, that is, in the positive pressure chamber, is there a possibility of blockage? If there is blockage in the positive pressure chamber and fluctuations occur, it should be pressure fluctuations within the tower that cause such fluctuations.
The pressure in the distillation tower is between 0.4 and 0.6 MPa; the pressure tapping line is a pipeline that was built by ourselves, without any additional flanges or capillaries.